Differential pressure gas lift valve

ABSTRACT

A subsurface well gas lift valve for incorporation in a tubing string disposed in a well bore and having a gas inlet choke or orifice for gas supplied through the well casing and an outlet into the tubing string, a piston valve being shiftable between open and closed positions to control gas flow between the inlet and outlet, the piston valve having a greater effective area subject to gas pressure on the downstream side of the inlet choke when in open position than its area subject to the tubing pressure when in closed position, permitting the choke to be of a greatly increased area, while maintaining a small difference between the pressure differential at which valve opening occurs and the pressure differential at which valve closing occurs.

United States Patent [72] Inventor David V. Chenoweth 2,345,865 4/1944 Boynton 137/155 Houston, Tex. 2,588,715 3/1952 Garrett 137/155 [21] Appl. No. 764,738 2,668,554 2/1954 Seyffert 137/ 155 [22] Flled 1968 Primary Examiner-Alan Cohan [45] Patented Feb. 2, 1971 Atmmey Bemard Kriegel [73] Assignee Baker Oil Tools, Inc.

Commerce, Calif. a corporation of California ABSTRACT: A subsurface well gas lift valve for incorporation V [54] DIFFERENTIAL PRESSURE GAS LIFT VALVE in a tubing string disposed in a well bore and a gas inlet 9 chain, 10 Drawing Figs. choke or orifice for gas supplied through the well casing and an outlet Into the tubing string, a piston valvebemg'shlftable 52 U S Cl 37 l 155, between open and closed positions to Conn-0| gas fl 103/232 between the inlet and outlet, the piston valve having a greater [Iateffective area subject to gas pressure on the downstream side [50] Field of Search 137/155; f the inlet choke when in open position than its area Subject 103/232 to the tubing pressure when in closed position, permitting the choke to be of a greatly increased area, while maintaining a [56] UNITESZETES IZTFFENTS sniall difference between1 the pressure gigerentia: at W216;

va ve opening occurs an t e pressure i erentia at w ic 2,312,315 3/1943 Boynton 137/155 valve closing occurs.

27 28 A: aw/ v 34 5/ f A: 29/

DIFFERENTIAL PRESSURE GAS LIFI VALVE The present invention relates to differential gas lift valves, which are used to inject high pressure gas into a tubing string disposed in a well bore for the purpose of displacing or aerating the liquid in the tubing string and to lift the liquid to the surface or top of the well bore In prior gas lift systems, the fluid column in the tubing is aerated with supply gas forced into the casing string surround ing the production tubing, for the purpose of lifting the liquid column in the tubing above the point of gas injection to the surface, and also for the purpose of reducing the bottom hole pressure sufiiciently to induce flow of the well production into the well bore and upwardly into the tubing string. A prior art differential gas lift valve A is disclosed in FIG. 9 of the drawings of the present application. With this valve, supply gas in the tubing-casing annulus discharges through one or a plurality of orifices 10 into the valve body, and when the valve is in opened condition, such gas flows through a valve seat 11 and is discharged into the tubing string T The supply gas pressure is acting over an effective cross-sectional area of a piston valve 12, which area is designated in FIG. 9 as A,. The pressure in the tubing string is acting downwardly over the area A, of the piston when the valve is closed, and this pressure, which is normally substantially lower then the gas pressure in the tubing-casing annulus, has its force tending to open the valve supplemented and assisted by the force of a spring 13 engaging the piston valve member.

All of the prior valves have been designed with the area A, equal to the area A,,. Accordingly, such valves will open when the tubing pressure P, times the area A,, plus the force of the spring 13, exceeds the gas pressure P times the area A,,. When the valve is in its open condition, the pressure P on the downstream of the orifices 10 times the area A,,, plus the spring force, must exceed the gas pressure P acting over the area A,,. With the valve in the open condition, the gas discharging through the orifices lifts the liquid in the tubing string to the surface. As it does so, the pressure P, decreases to the point at which the gas pressure P acting over the area A, will overcome the force of the spring and the force of the pressure I acting over the area A,., to shift the valve to the closed condition. Stated in another manner, assuming the valve to be in the closed position, it will open when the liquid level in the tubing string rises to the point at which the pressure differential P, minus P, has decreased to the point at which the spring 13 can shift the piston valve 12 to its open condition. The valve will shift from the open to the closed position when the pressure difierential I, minus P, increases to the point at which the force of the spring is overcome.

When used for intermittent liquid expulsion efficiency in elevating the liquid in the tubing string to the top of the well bore, the total orifice or choke area A should be as large as is practical. and there must be a small difference between the pressure differential I minus P effecting opening of the valve, and the pressure I minus P,,, effecting closing of the valve; that is to say, there must be a small spread between the opening pressure differential and the closing pressure differential. In addition, the valve seat against which the piston valve seats must be bubble tight; that is to say, leakage should not occur with the valve in closed position.

The differential gas lift valve disclosed in FIG. 9 can only secure a small spread between the opening and closing differentials when P, is fairly close to P,. This desirable small spread or relationship can only occur when the total area through the chokes or orifices I0 is quite small when compared with the valve seat area A," If large choke areas were used, the differential gas lift valve will have a considerable undesirable spread in differential pressures.

By virtue of the differential gas lift valves hereinafter described, a greatly increased choke or orifice area A, can be used, and yet a "small spread" between the opening and closing pressure differentials obtained. This is done by making the area A, of the piston valve, over which the gas pressure in the tubing-casing annulus acts. larger than the area A of the valve seat. Such larger area compensates for the smaller closing pressure drop created by the use of the enlarged choke or chokes. It will be apparent that, with larger orifice areas. the pressure drop through each orifice is smaller, and. consequently, the valve will be shifted from an open to a closed condition when the pressure differential P, minus P is developed. Thus, the pressure differential at which closing occurs will be different from the pressure differential P, minus P, at which valve opening occurs by only a small amount.

With the use of the large orifice area, a much greater gas flow can occur to move the liquid slug in the tubing string T to the top of the well bore.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIG. 1 is a diagrammatic view of a well installation embodying gas lift valves;

FIG. 2 is a longitudinal section through a gas lift valve embodying the invention in open condition;

FIG. 3 is a view similar to FIG. 2 with the valve in closed condition;

FIGS. 4a and 4b together constitute a longitudinal section through another form of gas lift valve apparatus, FIG. 4b being a lower continuation of FIG. 4a;

FIG. 5 is a partial longitudinal section through the specific gas lift valve illustrated in FIGS. 4a and 4b, on an enlarged scale, with the valve in open condition;

FIG. 6 is a view corresponding to FIG. 5, with the valve in closed condition;

FIG. 7 is a cross section taken along the line 7-7 on FIG. 4b;

FIG. 8 is a partial longitudinal section similar to FIG. 5 of yet another embodiment of the invention, with the valve in open condition; and

FIG. 9 is a longitudinal section through a prior art gas left valve.

A system embodying the differential gas lift valves illustrative of the present invention is disclosed in FIG. 1, which diagrammatically represents an oil well W having a casing string B therein, with fluid from a production zone C capable of passing through casing perforations D to the casing interior. A well packer E is set in the casing string above the perforations, and a tubing string T is disposed in leakproof relation to the packer so that formation fluid can flow upwardly through the tubing string to the top of the well bore, the tubing string extending in sealed: relation through a casing head G and into a production line H under the control of a surface valve J.

A lowermost gas lift valve is mounted on the tubing string to control the injection of gas within the casing-tubing annulus K, which is supplied from a suitable compressor or supply line through the gas line L into the upper portion of the casing string, there being a suitable valve M for controlling such flow of gas. A series of spaced preset gas lift valves 101 may also be installed along the tubing string T at predetermined intervals, these gas lift valves 101 above the lowermost valve 100 normally being used only for initially unloading the liquid in the casing-tubing annulus K down to the lowermost gas lift valve 100, and also for initially partially unloading the liquid in the tubing strihg, so that the valve IOQ can thereafter intermittently or continuously aerate the liquid column in the tubing string T and raise it to the top of the well bore and into the production line H. After the initial lowering of the liquid level in the tubing string to the desired level, the gas lift valves 101 above the lowermost valve will close, the lowermost valve 100 being the only one necessary for continuously or intennittently unloading the tubing of the production fluid therein. inasmuch as a differential control valve N will prevent the liquid level or pressure in the tubing string T from rising to a point at which the liquid cannot be discharged from the tubing string by the supply gas in the casing-tubing annulus K. The differential control valve N may be any of the specific designs illustrated in my application for "Diflerential Pressure Liquid Level Control Apparatus." filed Sept. 19. 1968, Ser. No.

760,883, now US Pat. No. 3,506,379.

The difi'erential gas lift valve 100 disclosed in FIGS. 2, 3 is mounted on the exterior of the tubing string T. A fitting is suitably secured, as by welding, to the exterior of the tubing string and has its internal passage 21 communicating with the interior of the tubing string through a slotted port 22 The lower portion 23 of the fitting is internally threaded for threaded attachment of a differential gas lift housing 24 thereto, which has an upwardly facing valve seat 25 adapted to be engaged by a ball check valve element 26 to prevent reverse flow of fluid from the tubing string T into the tubingcasing annulus K, this housing also having a cylindrical valve seat 27 with an area A, adapted to be closed by the upper valve head portion 28 of a piston valve member 29 slidably mounted in the inner bore of the housing below a plurality of side chokes or orifices 30 opening through the wall of the housing below the valve seat 27. Upward movement of the piston valve 29 is limited by engagement of its shoulder 31 with a companion downwardly facing shoulder 32 on the housing, at which time the valve head 28 will be disposed within the cylindrical seat 27, leakage of fluid between the head and seat being prevented by a suitable side seal ring 33 mounted in a groove 34 in the head and sealingly engaging the valve seat 27. When the valve head 28 is sealingly engaged with the seat, the head itself has engaged the ball check valve member 26 and elevated it from its companion valve seat 25 (H0. 3), so that the fluid pressure P, in the tubing string can act in a downward direction over the area A, of the valve head.

As illustrated in FIG. 2 of the drawings, the piston valve member 29 is shiftable downwardly to a position in which its valve head 28 is completely removed from the valve seat 27, opening the chokes 30 to the passage of gas from the tubingcasing annulus K, through the valve seat 27 and into the tubing string T. Downward movement of the piston valve is limited by engagement of a downward facing piston shoulder 35 with a suitable stop ring 36, in the form of a split snap ring, mounted within an internal groove 37 in the lower portion of the valve housing 24. Such downward shifting of the valve head occurs as a result of the combined action of the fluid pressure P, in the tubing string acting downwardly over the area A, of the piston valve and a tension spring 38, the upper end of which is suitably connected to the lower end of the piston valve 29, the lower end of the spring being suitably connected to a spring anchor member 39 welded, or otherwise attached, to the exterior of the tubing string T. the spring being protected by a suitable enclosure 40. When the piston valve member 29 is in its downward or full port opening position, the spring 38 may have very little tension in it. However, when the valve is in its closed position, the spring may have substantial tension.

It is to be noted that the gas pressure in the tubing-casing annulus K acts in an upward direction over the area A, of the piston valve, which area is much greater than the area A, of the upper valve head portion 28 of the piston valve. When the valve is closed, the gas pressure is also acting in a downward direction over the annular area A, of the large diameter piston portion 41, which is the area between the cylindrical valve seat 27 and the larger diameter surface 42 of the cylindrical portion of the housing in which the piston slides. This pressure is designated P, in the drawings. When the valve is in the closed condition, the gas pressure can still pass through the chokes 30 to the interior of the housing above the piston shoulder 43 having part of the area A and act downwardly on the piston valve 29. The gas pressure acting over this area A, makes the resultant area over which the gas pressure acts, with the valve in the closed condition, the same area A as the area A, of the seat 27 of the gas'lift valve. That is, A, A A,.

Thus, with the valve inthe closed condition, the tubing pressure P, is acting downwardly over the area A,., tending to shift the piston valve to open position. The gas pressure in the tubing-casing annulus K is acting upwardly over the area A, A or A,., tending to maintain the piston valve 29 in the closed position. The spring 38 is acting over the piston valve in a downward direction, supplementing the force of the tubing pressure and tending to shift the valve downwardly to open position. When the liquid level in the tubing string has risen sufficiently, so that its downward force on the piston valve supplemented by the spring force exceeds the force of the gas pressure acting upwardly on the piston valve, the piston valve will be shifted downwardly to an open condition, and the gas under pressure can then flow through the open ports 30 and through the valve seat 27 and past the ball check valve element 26, through the tubing port 22 to the interior of the tubing string T, lifting the slug or column of liquid ahead of it to the top of the well bore. The gas pressure P, within the valve housing 24 on the downstream side of the orifices 30, which will be less than the gas pressure P, in the tubing-casing annulus K, because of the throttling action of the orifices 30, will then be acting in a downward direction on the piston valve 29 over its full area A,, this force being supplemented by the force of the spring 38, which can then be rather low, to maintain the piston valve member in the open condition (FIG. 3). However, as the slug of liquid is discharged at the top of the well bore, the flow of gas through the orifices 30 accelerates, the gas pressure P, on the downstream side of the orifices and acting downwardly on the piston valve 28 decreasing, until it and the spring 38 are insufficient to hold the valve 29 in the downward or valve opening condition, the greater gas pressure in the tubing-casing annulus K acting upwardly over the area A, of the piston valve shifting it to the'closed condition (H0. 2).

By making the area A, over which the gas pressure P, acts with the valve in the open condition greater than the area A, over which the tubing pressure P, acts when the valve is in the closed condition, the area A, of the orifices or chokes 30 can be made much greater, since the larger piston area A, compensates for the smaller closing pressure drop created by the enlarged choke or orifice area A,.. Thus, there is still provided a differential valve that will open and close at approximately the same differential pressure.

In the operation of the gas lift valve disclosed in FlGS. 2, 3, let it be assumed that it is used in connection with the differential pressure liquid control valve N installed in the tubing string T just below the gas lift valve and above the well packer E, and also that the tubing-casing annulus K has been unloaded down to the location in the gas lift valve 100, the liquid level in the tubing string T also having reached a level in the tubing string at which the tubing pressure P, plus the spring force opens the gas lift valve 100. The gas under pressure can then flow through the orifices 30 and through the gas lift valve into the tubing string T to lift the liquid to the top of the well bore. As the liquid is being discharged, the velocity of gas through the orifices increases and the pressure P, inside the valve body 24 and on the downstream side of the orifices 30 will decrease to the point at which the gas pressure P, in the tubing-casing annulus K will shift the valve to a closed condition. Despite the use of the larger area chokes or orifices 30, the pressure differential required to close the valve will be approximately the same as the pressure differential between the gas pressure P, and the tubing pressure P, to open the valve, the small spread" between the two pressure differentials being due to the fact that the greatly increased area of the chokes or orifices 30 is compensated for by the fact of the area A of the piston valve over which the gas pressure P, act is substantially larger than the area A, of the valve seat 27.

The gas lift valve willreniain closed until the liquid level in the tubing string T has again risen to the point at which the tubing pressure P, plus the spring force can overcome the force of the tubing-casing annulus gas pressure P, acting over the differential area A of the piston valve 29 A, A when it is in the closed condition. and the foregoing cycle of operation will be repeated In the embodiment of the invention illustrated in FIGS. 4 to 7, the differential gas lift valve IS located within the tubing string T itself, substantially at the location of the valve 100 in FIG. 1. As disclosed, the tubing string includes a section 50 having an upper threaded box 51 threadedly secured to the tubing section 52 thereabove, and a lower pin 53 threadedly secured to a nipple 54. which is in sealed relation to the packer E anchored in packed-off condition in the well casing above the casing perforations D. The gas lift mechanism includes an outer housing structure 55. consisting of an upper packing section 56 carrying an upper packing 57, and a lower packing section 58 carrying a lower packing 59. The upper packing section 56 is threadedly secured to an intermediate section 60, the lower end of which is threadedly attached to a crossover sub 61. which is. in turn, threadedly secured to the lower packing section 58. The upper packing section 56 has the mandrel 62 of a lock assembly 63 secured thereto, this mandrel holding the upper packing 57 in place. The lower packing 59 is held in place between the lower packing section 58 and the crossover sub 61 The lock mandrel 62 carries pivoted latch dogs 64 which are shifted outwardly by springs 65 into a circumferential locking groove or recess 66 in the tubing section 50 when a shoulder 67 on the lock mandrel engages a companion shoulder 68 on the housing section 50. At this time, the upper and lower packings 57, 59 are disposed on opposite sides of gas inlet ports 69 extending through the tubing section 50 and establishing communication between the tubing-casing annulus K above the well packer E and the interior of the tubing section or housing 50.

An inner housing 70 is located within the outer housing 55 in spaced relation thereto. The lower end of the inner housing is threadedly secured to a lower cage 71, which is, in turn, threadedly attached to the upper portion 72 of the crossover sub 61. The upper end of the inner housing 70 is threadedly attached to an upper cage 73 that has a lower threaded box 74 to which the housing 75 of the differential gas lift valve mechanism 101a is secured. This differential gas lift valve mechanism is essentially the same as the one 100 described in connection with the form of invention illustrated in FIGS. 2, 3, and includes a valve piston 29 slidable within the differential housing 75 and having an upper head 28 adapted to be disposed within a cylindrical valve seat 27, the upward limit being determined by engagement of a shoulder 31 on the piston with the downwardly facing shoulder 32 on the housing. When engaged with this seat, the valve head 28 holds a ball check valve member 26 elevated above its companion valve seat 25. A tension spring 38 is connected at its upper end to a depending portion 29a of the valve piston, with its lower end connected to a crosspin 76 secured to a spring tube 40a surrounding the spring and suitably secured. as by welding or brazing, to the lower end of the differential housing 75.

The differential valve housing 75 and the spring tube 40a are located in spaced relation to the inner wall of the inner housing 70, the upward movement of the ball valve member 26 from its seat being limited by its engagement with a ball stop pin 77 extending across the passage through the upper cage 73 above the ball. When the gas lift apparatus is located in the tubing section 50 with its latches 64 expanded into the locking groove 66, the gas under pressure from the tubing-casing annulus K can pass through the tubing section ports 69 to an internal groove 78 in the section and thence inwardly through gas ports 79 extending through the crossover sub 61 and communicating with a central passage 80 in the sub. the gas then being capable of flowing upwardly through the lower cage 71, unseating a ball check valve 81 from its companion valve seat 82 and flowing upwardly into the inner housing 70 below the differential gas lift valve 101a. The gas can then flow through the orifices or chokes 30 in the housing 75 immediately below the cylindrical valve seat 27. and upwardly through the seat to the interior of the upper cage 73, passing upwardly through the latter into the upper packing section 56 and through the tubular mandrel 62 of the lock assembly 63 into the tubing string T thereabove. At the same time, the well production is capable of flowing upwardly from the casing below the well packer E into the tubing nipple 54 and then into the lower packing section 58, from where it will flow through circumferentially spaced longitudinal passages 84 in the crossover sub 61 into the annulus 85 between the inner housing 70 and the outer housing 55. From theupper end of this annulus 85, the well production can flow around the upper end of the upper cage 73 and into the passage through the upper packing section 56, continuing on up through the lock mandrel 62 into the tubing string T thereabove. It desired, the differential control valve N can be incorporated in the tubing string T below the gas lift valve apparatus.

When the differential gas valve opens, the gas under pressure flowing through the open ports 30 will carry the well production upwardly through the tubing string T and to the top of the well bore.

The area relationships of the differential gas lift valve 101a disclosed in FIGS. 4 to 7 is the same as in the other embodiment of the invention shown in FIGS. 2, 3, and the same designation has been applied to the valve piston portions and the valve seat, as well as to the chokes or orifices. The mode of operation of the apparatus is the same as described above in connection with FIGS. 2, 3.

With the apparatus disclosed in FIGS. 4 to 7, it can be run in through the tubing string T and can also be retrieved therefrom. A suitable retrieving tool (not shown) can be run in on a wire line through the tubing string T and will engage the latches 64 to retract them from the lock groove 66, as well as becoming coupled to the upper neck of the mandrel 62. The specific lock assembly and manner of retrieving the equipment through the tubing string form no part of the present invention and is fully described in US. Pat. No. 2,855,007.

In the form of invention disclosed in FIG. 8, the intermittent gas lift valve 100a shown in FIGS. 4 to 7 has been replaced by a continuous gas lift valve l00b. The continuous gas lift valve is the same as the other valve, except that it has a central orifice or choke passage running through it through which gas can flow continuously when the valve is closed. When the valve is opened, the relatively large area side orifices 30 come into play to provide a greater gas flow area for unloading the liquid in the tubing string T, until the casing-to-tubing differential pressure P, P, increases sufficiently to close the valve. so that the gas can then continue to flow through the smaller area orifice or choke 95 for normal operation. This choke 95 is of relatively small size and its use is desirable in some instances to secure efficient continuous lift of fluid in the tubing string T, which passes through the differential control valve N, into the annular passage 85 between the inner and outer housings, and then into the tubing string T thereabove.

As in the other forms of the invention, the area relationships between the piston 2%, its valve head 28, the valve seat 27, and the side chokes or orifices 30 are the same, the valve operating in the same manner, so that a lesser pressure drop can occur through the side orifices 30 when they are open for effective and rapid lifting of the liquid in the tubing string T to the surface, and yet provide a much smaller difference in the pressure differential at which the gas lift valve will close as compared to the pressure differential between the casing and tubing at which the valve will open.

Iclaim:

1. In apparatus for lifting fluid in a tubular string disposed in a well bore having a prodiicing formation:

a valve housing having a passage communicable with the. in-

terior of the tubular string and also having a valve seat surrounding said passage; said housing having one or more orifices through which a gaseous fluid under pressure can flow into the housing and through said valve seat; a valve member shiftable in said housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of the housing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubing string when the valve member is engaged with said seat tending to shift said valve member toward its open position. and a third surface subject to the pressure of the gaseous fluid in the housing between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being substantially greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member tending to shift said valve member toward open position.

2. In apparatus as defined in claim 1; said valve member having a central orifice passage through which said gaseous fluid externally of said housing can flow into the tubing string when said valve member is engaged with said seat.

3. In a tubular string disposed in a well bore having a producing formation: a tubular member connectable to the tubular string and having passage means through which production fluid from the formation can flow upwardly into the tubular string; a valve housing mounted in the interior of said tubular member and having a passage communicating with said passage means and also having a valve seat surrounding said passage; means for conducting a gaseous fluid under pressure from the exterior of said tubular member to said valve seat for flow therethrough into said passage, said conducting means including one or more orifices in said housing on the upstream side ofsaid seat; a valve member shiftable in said housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of the housing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubular string when the valve is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the housing between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member tending to shift said valve member toward open position.

4. In apparatus as defined in claim 3; wherein said valve member is a piston slidable in said housing axially to and from said valve seat.

5. In apparatus as defined in claim 3; wherein said valve member is a pistonslidable in said housing axially to and from said valve seat; said su plemental means comprising a spring.

operatively connected 0 said piston; said piston having a central orifice passage through which the gaseous fluid externally of said housing can flow into said passage when said piston is engaged with said seat.

6. ln apparatus for lifting fluid in a tubular string disposed in a well bore having a producing formation: a tubular section adapted to form part of the tubular string; an outer housing mounted in said section; an inner housing in said outer housing, said housing providing passage means through which the production fluid from the formation can flow upwardly and into the tubular string; a valve housing mounted in said inner housing and having a passage communicating with said passage means and also having a valve seat surrounding said passage; means for conducting a gaseous fluid under pressure from the exterior of said tubular section to the interior of said inner housing and to said valve housing; said valve housing having one or more orifices through which the gaseous fluid in the inner housing can flow into said valve member and through said valve seat; a valve member shiftable in said valve housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of .the valvehousing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubular string when the valve member is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the valve housing between said valve'seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being substantially greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member to shift said valve member toward open position.

7. In apparatus as defined in claim 6; means releasably mounting said inner and outer housings, valve housing, valve member and supplemental means in said tubular section for withdrawal from said section through the tubular string to the top of the well bore.

8. In apparatus as defined in claim 6; wherein said valve member is a piston slidable in said housing axially to and from said valve seat. I

9. ln apparatus as defined in claim 6; wherein said valve member is a piston slidable in said valve housing axially to and from said valve seat; said supplemental means comprising a spring operatively connected to said piston; said piston having an orifice passage through which a gaseous fluid can flow when said piston is engaged with said seat. 

1. In apparatus for lifting fluid in a tubular string disposed in a well bore having a producing formation: a valve housing having a passage communicable with the interior of the tubular string and also having a valve seat surrounding said passage; said housing having one or more orifices through which a gaseous fluid under pressure can flow into the housing and through said valve seat; a valve member shiftable in said housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices frOm flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of the housing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubing string when the valve member is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the housing between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being substantially greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member tending to shift said valve member toward open position.
 2. In apparatus as defined in claim 1; said valve member having a central orifice passage through which said gaseous fluid externally of said housing can flow into the tubing string when said valve member is engaged with said seat.
 3. In a tubular string disposed in a well bore having a producing formation: a tubular member connectable to the tubular string and having passage means through which production fluid from the formation can flow upwardly into the tubular string; a valve housing mounted in the interior of said tubular member and having a passage communicating with said passage means and also having a valve seat surrounding said passage; means for conducting a gaseous fluid under pressure from the exterior of said tubular member to said valve seat for flow therethrough into said passage, said conducting means including one or more orifices in said housing on the upstream side of said seat; a valve member shiftable in said housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of the housing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubular string when the valve is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the housing between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member tending to shift said valve member toward open position.
 4. In apparatus as defined in claim 3; wherein said valve member is a piston slidable in said housing axially to and from said valve seat.
 5. In apparatus as defined in claim 3; wherein said valve member is a piston slidable in said housing axially to And from said valve seat; said supplemental means comprising a spring operatively connected to said piston; said piston having a central orifice passage through which the gaseous fluid externally of said housing can flow into said passage when said piston is engaged with said seat.
 6. In apparatus for lifting fluid in a tubular string disposed in a well bore having a producing formation: a tubular section adapted to form part of the tubular string; an outer housing mounted in said section; an inner housing in said outer housing, said housing providing passage means through which the production fluid from the formation can flow upwardly and into the tubular string; a valve housing mounted in said inner housing and having a passage communicating with said passage means and also having a valve seat surrounding said passage; means for conducting a gaseous fluid under pressure from the exterior of said tubular section to the interior of said inner housing and to said valve housing; said valve housing having one or more orifices through which the gaseous fluid in the inner housing can flow into said valve member and through said valve seat; a valve member shiftable in said valve housing between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid; said valve member having a first surface subject to the pressure of the gaseous fluid externally of the valve housing tending to shift said valve member toward its closed position, a central second surface subject to the pressure of the fluid in the tubular string when the valve member is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the valve housing between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat; the area of said first surface and said third surface each being substantially greater than the area of said second surface; said third surface consisting of said central second surface and an annular fourth surface extending laterally outwardly of said second surface when said valve member is in closed position; said fourth surface being in unrestricted communication with the housing space between said valve seat and one or more orifices and being substantially equal in area to the difference between said first surface and central second surface; and supplemental means exerting a force on said valve member to shift said valve member toward open position.
 7. In apparatus as defined in claim 6; means releasably mounting said inner and outer housings, valve housing, valve member and supplemental means in said tubular section for withdrawal from said section through the tubular string to the top of the well bore.
 8. In apparatus as defined in claim 6; wherein said valve member is a piston slidable in said housing axially to and from said valve seat.
 9. In apparatus as defined in claim 6; wherein said valve member is a piston slidable in said valve housing axially to and from said valve seat; said supplemental means comprising a spring operatively connected to said piston; said piston having an orifice passage through which a gaseous fluid can flow when said piston is engaged with said seat. 